A driveline of a hybrid vehicle may include and engine and a motor. The motor and the engine may be selectively mechanically coupled to increase driveline output or to operate the motor and/or the engine more efficiently. The motor may provide torque to propel the vehicle or it may convert driveline rotational energy into electric energy. The engine may provide torque to propel the vehicle or it may provide torque to convert into electrical energy. However, it may be challenging to control driveline torque in a vehicle where multiple torque sources are providing torque to the vehicle driveline during varying driving conditions.
The inventors herein have recognized the above-mentioned issues and have developed a method for operating a hybrid powertrain, comprising: operating an engine and a motor to supply torque to a driveline; and supplying a transmission input shaft torque solely via the motor in response to a driving surface coefficient of friction is less than a threshold value.
By solely supplying torque from a motor to a transmission input shaft during slick road conditions, it may be possible to better control wheel slip. For example, a motor can supply torque to the transmission at a very low speeds so that wheel spin may be reduced. Additionally, torque delivery at lower transmission input shaft speeds may be smoother with the motor than the engine further reducing the possibility of wheel slip. In one example, the driving surface coefficient of friction may be estimated and the motor may be operated as the sole torque input source to the transmission based on the estimated coefficient of friction.
The present description may provide several advantages. Specifically, the approach may improve vehicle traction on driving surfaces that have a low coefficient of friction. Additionally, the approach may reduce driveline wear by reducing a number of engagements of a disconnect clutch.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.